Smoke from biomass combustion leads to approximately 1.6 million excess annual deaths and a substantial share of the global burden of disease, due in large part to increased risk of acute lower respiratory infections (ALRI) in children under age five. Recent evidence also suggests that exposures to cook smoke during pregnancy may be associated with reduced birth weight. This issue is particularly relevant in sub-Saharan Africa, where cooking with biomass fuels is widespread. The overall goal of the proposed research is to test the effectiveness of commercially available, low cost improved cook stoves in improving infant health outcomes from birth through six months of age. Two hypotheses will be tested: Hypothesis 1. Use of improved cook stoves starting by the third trimester pregnancy will lead to a significant increase in average birth weight in newborns. Hypothesis 2: Use of improved cook stoves will lead to a significant reduction in the rate of severe ALRI during the first six months of life. These hypotheses will be tested in a randomized intervention trial among 800 maternal- infant pairs in the Kintampo district of rural Ghana in West Africa. Pregnant women who are primary cooks in their families will be identified before the third trimester of pregnancy. We will randomly assign villages, matched on average assets, to early or late intervention groups. Within the early intervention villages, improved cook stoves will be distributed to enrolled pregnant women, along with health insurance and an insecticide-treated bed net. The late intervention group will receive insurance and a bed net at enrollment, and the full intervention at the completion of the postnatal follow-up. Gestational age will be determined by sonogram upon enrollment and provide confirmation that potential subjects are carrying live singleton fetuses. We will assess real-time personal exposure to carbon monoxide (CO) among all subjects during pregnancy and during the neonatal period. At birth we will measure birthweight and collect a placental smear for malaria assessment. Field workers will monitor for severe pneumonia at weekly intervals in the home for the first six months of the life of a child based on the Integrated Management of Childhood Illness (IMCI) guidelines, with clinical referral of cases. The proposed research builds on an established collaboration between Columbia University and the Kintampo Health Research Center in central Ghana.